The delivery of radio frequency (RF) energy to target regions within solid tissue is known for a variety of purposes of particular interest to the present invention. In one particular application, RF energy may be delivered to diseased regions (e.g., tumors) for the purpose of ablating predictable volumes of tissue with minimal patient trauma.
RF ablation of tumors is currently performed using one of two core technologies. The first technology uses a single needle electrode, which when attached to a RF generator, emits RF energy from the exposed, uninsulated portion of the electrode. This energy translates into ion agitation, which is converted into heat and induces cellular death via coagulation necrosis. The second technology utilizes multiple needle electrodes, which have been designed for the treatment and necrosis of tumors in the liver and other solid tissues. U.S. Pat. No. 6,379,353 discloses such a probe, referred to as a LeVeen Needle Electrode™, which comprises a delivery cannula and an electrode deployment member reciprocatably mounted within the delivery cannula to alternately deploy an electrode array from the delivery cannula and retract electrode array within the delivery cannula. The individual electrodes within the array have spring memory, so that they assume a radially outward, arcuate configuration as they are deployed from the delivery cannula. In general, a multiple electrode array creates a larger lesion than that created by a single needle electrode.
When creating lesions using an ablation electrode element (whether a single needle electrode or needle electrode array, deployable or otherwise) RF energy is commonly delivered to the tissue in one of several ways. In one arrangement, RF current may be delivered to an ablation electrode element in a monopolar fashion, which means that current will pass from the ablation electrode element to a dispersive electrode attached externally to the patient, e.g., using a contact pad placed on the patient's flank. In another arrangement, the RF current is delivered to two electrodes in a bipolar fashion, which means that current will pass between “positive” and “negative” electrodes in close proximity to each other, e.g., two electrodes on the same probe or array or on different probes or arrays. Bipolar arrangements, which require the RF energy to traverse through a relatively small amount of tissue between the tightly spaced electrodes, are more efficient than monopolar arrangements, which require the RF energy to traverse through the thickness of the patient's body. As a result, bipolar ablation probes generally create larger and/or more efficient lesions than monopolar ablation probes. Additionally, bipolar arrangements are generally safer for the physician and patient, since there is an ever-present danger that the physician and patient may become a ground in the monopolar arrangement, resulting in painful burns.
Currently, bipolar LeVeen-type ablation probes, which comprise two axially arranged deployable electrode arrays (a proximal electrode array and a distal electrode array), are being developed in order to combine the advantages that accompany the use of electrode arrays and bipolar ablation. Details regarding the structure and operation of such bipolar ablation probes are disclosed in U.S. Patent Publication 2002/0022864, entitled “Multipolar Electrode System for Radiofrequency Ablation,” and U.S. patent application Ser. No. 09/663,048, entitled “Methods and Systems for Focused Bipolar Tissue Ablation,” both of which are expressly incorporated herein by reference.
In a typical tumor diagnostic and therapeutic procedure, tissue suspected of containing an abnormality is imaged using a high definition imaging modality, such as Magnetic Resonance Imaging (MRI). If an abnormality, such as a tumor, is discovered, a sample of the abnormal tissue is retrieved. This is typically accomplished by percutaneously introducing a biopsy needle through healthy tissue into contact with the abnormal tissue. Proper guidance and placement of the biopsy needle is facilitated by the use of a standard imaging modality, such as fluoroscopy or computed tomography (CT). The biopsy needle, with the tissue sample, is then removed from the patient's body, and the tissue sample is placed into a container and sent to a laboratory to examine whether it is malignant or benign. In the interim, the physician and/or patient may decide to treat the tumor, whether or not the tumor is actually malignant or benign. In this case, the abnormal tissue would typically be treated immediately after performing the biopsy. Alternatively, the physician and/or patient may decide to treat the tumor only if it is indeed malignant, in which case, such malignancy would be treated after receiving the laboratory results.
In either case, the tumor can be treated by percutaneously introducing an RF ablation probe through the patient's body into contact with the tumor in a similar manner that the biopsy needle was described above. The ablation probe can then be operated to ablate the tumor. The interstitial space left by the removal of the tumor can then be treated with a therapeutic agent, such as a drug. Typically, this is accomplished by introducing a separate drug delivery device into the patient's body in the same manner as the biopsy needle and ablation probe was, and delivering the drug into the interstitial space.
In performing the diagnostic/therapeutic procedure, the biopsy stylet, RF ablation probe, and drug delivery device can either be percutaneously introduced into the patient's body as stand-alone devices or as parts of a co-access delivery system. In the former case, each device may follow a different path than the devices before it, and thus must be meticulously delivered to the targeted region in the patient's body under an imaging modality, such as fluoroscopy and/or CT. The multiple tissue insertions also increases the pain and discomfort suffered by the patient during this procedure. When a co-access delivery system is used, however, each device is delivered through a single cannula that advantageously provides a more accurate delivery of the devices to the targeted region. That is, after the biopsy stylet has been delivered through the cannula and a biopsy is taken from the center of the targeted region, the cannula provides a convenient place marker for subsequently delivery of the ablation probe and drug delivery device to the targeted region without the need for navigational imaging. The use of a co-access delivery system also only requires a single percutaneous insertion, i.e., insertion of the cannula.
While a co-access system works well for monopolar ablation electrodes, such as the monopolar LeVeen Needle Electrode™, the currently existing co-access systems would not work well with bipolar ablation electrodes, such as the dual-electrode arrays disclosed in U.S. Patent Publication 2002/0022864 and U.S. patent application Ser. No. 09/663,048. This is largely due to the fact that it is desirable to locate the proximal and distal electrode arrays of the ablation probe on the respective proximal and distal fringes of the treatment region, so that the entirety of the abnormal tissue contained in the treatment region will be effectively treated during a single ablation procedure. To the extent that the electrode arrays must be re-navigated in order to ablate abnormal tissue that was not treated during the initial procedure, a main advantage of the co-access system will be lost—i.e., the cannula will no longer act as a place marker for properly locating the ablation probe, and unnecessary ablation procedures will have to be performed, increasing patient discomfort and increasing the time required to perform the procedure.
Notably, properly placement of the electrode arrays within the treatment region cannot be easily facilitated by merely modifying the length of the co-access cannula used to deliver the electrode arrays. For example, FIG. 1 illustrates a conventional co-access cannula 10 used to deliver proximal and distal electrode arrays 14, 16 of an ablation probe 12 into a tissue region TR. The cannula 10 has been shortened relative to the ablation is probe 12 in order to allow both electrode arrays 14, 16 to be deployed out from the distal end of the cannula 10. As can be seen, when the co-access cannula 10 is located, such that its distal tip resides within the tissue region TR, where the biopsy has previously been taken, the deployed electrode arrays 14, 16 will not be properly located within the tissue region TR. Instead, the proximal array 14 will be located near the center of the tissue region TR, and the distal array 16 will be located in the distal portion of the tissue region TR or distally outside of the tissue region TR. Thus, the proximal portion of the tissue region TR will not be treated when performing an ablation procedure with this arrangement—at least without having to proximally move the cannula 10 and ablation probe 12 and perform a second ablation procedure. Of course, if the cannula 10 is lengthened relative to the ablation probe 12, so that the electrode arrays 14, 16 can be properly located in the tissue region TR, the proximal electrode array 14, it will not be possible to deploy the proximal electrode array 14 out from the cannula 10.
Thus, there is a need for co-access ablation probe kits and methods that allow multiple bipolar electrode arrays to be properly deployed within a treatment region of a patient.